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This invention is directed to coatings for polymeric substrates, and in particular, the invention is directed to the application of an aqueous suspension of powdered silicone rubber to substrates useful in the manufacture of air bags for automobiles.
U.S. Pat. No. 4,594,134 (Jun. 10, 1986) teaches the use of powdered silicone rubber as a coating for various substrates including posters, butyl rubber, polyamides such as Nylon-6,6, and asphalt. The purpose of the coating is to remove surface tack of the substrate. However, the powdered silicone rubber in the ""134 patent is applied to the polymeric substrate as a dry powder, rather than as an aqueous suspension, and therefore surface coverage obtained in the ""134 patent is not uniformly consistent.
While application of aqueous dispersions of powdered silicone rubber to polymeric substrates such as silicone gel sheets is known in U.S. Pat. No. 4,985,277 (Jan. 15, 1991), the surface of the silicone gel sheet to which the aqueous dispersion is applied is cured rather than uncured. Therefore adherence of powdered silicone rubber to these substrates is difficult to maintain.
These disadvantages are overcome according to this invention by applying an aqueous suspension of powdered silicone rubber to polymeric substrates, especially polymeric substrates which have been pre-treated with a thermosetting liquid silicone rubber composition, and more particularly to polymeric substrates used as base fabrics in the manufacture of automobile air bags.
The invention therefore relates to a process for modifying the surfaces of polymer coated base fabrics used in the fabrication of coated articles such as automotive airbags, inflatable curtains, latex products, and other such inflatable devices, wherein the coefficient of friction needs to be minimized.
In particular, the invention consists of treating polymer coated base fabrics with an aqueous suspension of powdered silicone rubber which reduces the coefficient of friction, i.e., the tack, and renders the coated base fabric resistant to blocking.
The polymer coated base fabric may be treated with the powdered silicone rubber by a variety of techniques, some examples of which are electrostatic spraying, atomization of a solvent dispersion, atomization of an aqueous suspension, and by mechanical means such as buffing.
The resulting powdered silicone rubber modified and coated base fabric has been found to possesses a unique tack-free and slippery feel which has a low coefficient of friction, all of which properties are desirable attributes.
These and other features of the invention will become apparent from a consideration of the detailed description.